1. Field of the Invention
The present invention relates to an improved mechanical and electrical safety device for arming and detonating a fuze in ammunition and rendering the fuze inert under prearranged conditions.
2. Description of the Related Art
A number of safety devices and arming devices have been utilized on ammunition to prevent inadvertent detonations. For example, projectiles such as grenades, rockets, large caliber ordnance, and aircraft carried bombs have utilized various arming mechanisms which only arm the explosive device upon sensing appropriate accelerations and decelerations which would be characteristic of launch and impact with an intended target.
Some safe and arm devices are purely mechanical in nature, relying upon centrifugal effects. Typical mechanical devices are disclosed in U.S. Pat. No. 3,742,854; 4,796,532; and 4,869,172.
Other safe and arm devices have been designed to electronically sense launch, velocity, and impact, and in so doing, arm and detonate the main explosive charge. U.S. Pat. No. 3,359,904 issued to Nerheim, discloses a fuze which utilizes a piezoelectric crystal compressed by the set back forces on launch to produce a charge which is stored in a capacitor. Upon impact, a second piezoelectric crystal is compressed which generates a charge to actuate an electronic switch to discharge the capacitor previously charged upon launch.
Another electronic device, described in U.S. Pat. No. 3,653,324 issued to Ferlani et al, utilizes two transducers to sense the peculiar signature which results from a projectile launch. The first transducer is a set back sensing piezoelectric crystal and the second is a barrel exit sensing transducer. Upon receipt of a signal proportional to the correct launch acceleration followed by a signal representative of barrel exit, a switch is closed to actuate a separate arming device.
U.S. Pat. No. 3,808,975, discloses a piezoelectric crystal powered fuze circuit using a pair of back to back piezoelectric crystal cells in which the cells develop a potential upon acceleration of the projectile and then develop a reverse potential upon relaxation of the acceleration when the projectile emerges from the firing weapon. Thus, the piezoelectric cells sense projectile launch and muzzle exit to arm the device. A third piezoelectric cell or element is utilized to sense impact and detonate the device.
U.S. Pat. No. 3,850,102, issued to Mauro discloses a single piezoelectric crystal which is adapted to perform three functions. First, the crystal is compressed in one direction by the set back force of launch to produce a first voltage signal. During flight it senses the air impinging upon the launched projectile, thus generating a second lower voltage signal. Finally, it is compressed in the opposite direction upon impact to trigger the projectile detonation.
U.S. Pat. No. 3,967,555 issued To Gollick et al discloses a battery operated piezoelectric fuze which has a piezoelectric element to convert the mechanical shock of impact and into a detonator ignition signal. An arrangement of two diodes and a thyristor prevent detonator actuation if the shock wave produced upon impingement of the fuze is less than a threshold value to prevent unintended ignition but also provide ignition without there having been a response by the piezoelectric element such as upon impact. In this case, the piezoelectric element merely controls the switch between the battery power supply and the detonator.
In U.S. Pat. No. 4,723,087, a piezoelectric polymer ring is utilized to sense impact at virtually any angle and generate a voltage to ignite the detonating charge.
Another device, disclosed in U.S. Pat. No. 4,739,705 issued to Hudson et al, requires power from a missile battery. The accelerations of the missile due to an expulsion motor and a boost motor are sensed. In addition, Hall sensors are utilized in conjunction with an inertial wheel to provide a signal proportional to velocity and distance which after a predetermined distance, causes the detonator to be armed and aligned with the warhead stem.
Another example in which a piezoelectric crystal is used is disclosed in U.S. Pat. No. 4,848,234 issued to Farace et al. In this patent, a piezoelectric crystal is utilized to sense the spin rate of a projectile.
There remains a need for a fuze system which requires no external power or wires, has redundant safety features, and will reliably sense projectile launch and discriminate between launch and handling or mishandling accelerations and at the same time be able to render the projectile inert in the event that the intended target is not impacted after a successful launch mechanically arms the fuze.